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Reverse Osmosis

REVERSE OSMOSIS

Osmosis is the phenomenon of lower dissolved solids in water passing
through a semi-permeable membrane into higher dissolved solids water until
a near equilibrium is reached. Reverse Osmosis (RO) is a membrane process
of purification which removes the total dissolved solids (TDS) in water by
reversing the natural process of osmosis.
Pressure is applied to a TDS-concentrated solution against a
semi-permeable membrane, causing pure water to diffuse through the
membrane. RO has become an important process for a wide variety of
applications including: medical, laboratory, desalination, industrial
wastewater, DI pretreatment and drinking water.

TESTING RO WATER QUALITY
Electrical conductivity is the most convenient method for testing RO water
quality and membrane performance. Pure water is actually a poor electrical
conductor. The amount of ionized substances (or salts) dissolved in water
determines its conductivity. Normally, the vast majority of the total
dissolved solids in tap, surface or ground water are conductive
impurities.

Myron L® Company has conducted extensive research
relating conductivity to TDS, resulting in instrumentation and calibration
solutions which have become the standard of the RO industry.
When calibrating your conductivity instrument for testing fresh water, the
"442 Natural Water Standard™" solutions are the best choice. These
solutions are available in various concentrations. 442 solutions contain
the following salts diluted in pure water: 40% sodium bicarbonate, 40%
sodium sulfate and 20% sodium chloride. These are the most common salt
compounds in surface and ground water. A sodium chloride solution provides
better results in brackish or sea water because the predominant salt in
these waters is sodium chloride.

ORP
ORP (Oxidation Reduction Potential/Redox) and pH are important parameters
in measuring the success and useful life of an RO membrane. The ORP may be
used to determine the activity of an oxidizer. RO membranes are
susceptible to attack by oxidizers such as chlorine, bromine, ozone and
hydrogen peroxide. The activity of the oxidizer is more informative than
the chemical residual because it determines the ability and speed of
oxidation. A high ORP reading would indicate a need for pretreatment. A
low ORP may indicate biological activity which may cause fouling of the
membranes.

ORP can also be used to determine an overfeed of sodium bisulfate, which
is used to reduce chlorine. If the ORP reading is under 200 mV, you have a
reducing condition. This overfeed costs extra money and can lead to
environmental discharge problems. It is best to check the reject water,
where the concentration is highest. This will show even minute quantities
of oxidizers or reducers.

pH
pH is very useful in predicting membrane life and the scaling potential of
feed water. The higher the pH and calcium, the more likely it is that
scale will form on the membranes. However, with silicon based compounds, a
low pH will increase the tendency for scaling. Membranes also have a pH
range where operation is optimal. It is often useful to check the pH of
the reject water to help determine scaling potential.

RECOMMENDED INSTRUMENTATION:

HOME SYSTEM SALES
Since the early 1960's, the Myron L® Company has manufactured single and
multiple range hand-held instruments. Model RO-1 and RO-1NC are reliable,
single range instruments used to demonstrate the RO process to a
prospective buyer. The color coding of the model RO-1 dial dramatizes the
difference between high TDS (red-above EPA recommended limits for drinking
water) and low TDS (blue) RO water. Installers prefer the three range 532
models or the TechPro AR1 because they are ideal for accurately testing
both feed and product water.

COMMERCIAL / INDUSTRIAL
Larger RO systems such as those found in bottled water plants, hospitals,
industrial process, or seawater desalination require continuous monitoring
to verify water quality and membrane condition. For continuous measurement
of water quality, Myron L® manufactures the 750 Series II
Monitor/controllers. Monitor only and Monitor/controller are available.
Monitor and Monitor/controller models contain an adjustable set point and
a heavy-duty 10 amp relay which can be used to activate alarms, valves,
auto dialers, etc. A variety of options and outputs are available to cost
effectively tailor the monitor to the particular RO application.

The ULTRAMETERS™ 6P and 4P are preferred by water treatment professionals
for
calibrating and checking C/I RO systems. They appreciate the waterproof
case, 20 reading memory, and 3 preprogrammed TDS solution curves.
ULTRAMETERS are compact, but their multiple parameters give them the
versatility of several instruments.